Metal joist



Dec. 11, 1951 A. DAVIS, JR, ETAL 2,578,465

METAL JOIST Filed Oct. 7, 1946 s Sheets-Sheet 1 Dec. 11, 1951 A. DAVIS,JR., ETAL METAL JOIST 3 Sheets-Sheet '2 Filed Oct. 7, 1946 'Dec. 11,1951 A. DAvrs, JR, ETAL METAL JOIST 3 Sheets-Sheet 5 Filed Oct. 7, 1946Patented Dec. 11, 1951 METAL JOIST Augustine Davis, J r., and James A.Nichols, Washington, D. 0., assignors to Davisbilt Steel Joist, Inc.,Washington, D. 0., a corporation of Delaware Application October 7,1946, Serial No. 701,762

7 Claims.

This invention relates to building constructions, and more particularlyto metallic joists, trusses, beams, or girders and their associatedconnecting and supporting structures.

This application is a continuation-in-part of our copending applicationsSerial No. 583,948, filed March 21, 1945, and Serial No. 617,638, filedSeptember 20, 1945, both now abandoned.

The principal object of the invention is the provision of a novel andimproved metal joist for use in the erection of a wide variety ofbuildings, whether residential or commercial; one which is of relativelysimple construction, easy to manufacture at a relatively low costcomparable to that of wooden joists, and at the same time being of lightweight and capable of supporting heavy loads without deformation eitherby crushing, twisting, or bending.

It has long been known that wooden joists shrink across the grain thuscausing the flooring toseparate from the shoe strip and the door trim.The shrinking and warping of wooden joists causes plaster cracks andgives rise to sagging uneven floors, and this form of joist, thoughwidely used in expensive as well as low cost houses, is of coursegenerally inferior to steel joists.

Many prior proposals have been made looking. toward the substitution ofmetal joists for the conventional wooden ones, but such metal joists ashave been devised to meet the structural requirements of the variousbuilding codes, have been too expensive to manufacture in competitionwith wooden joists.

Furthermore, the attachment of the sub-flooring and of variousaccessories such as hangers,

bridging elements, furring, and the like, has, presented seriousproblems. A steel bar joist must conform to certain, requirements of theSteel Joist Institute Code and of building codes of all jurisdictions,both with respect to cross sectional area, weight per lineal foot, andcompression, torsional, and bending strength; and it has hitherto beenthought impossible to devise a metal joist having a top-chord membermade of nailable material (whether of nai-lable sheet steel or ofequivalent nailable gauge of other sheet metals), whereby the attachmentof flooring and accessories is facilitated, and at the same time being atrue structural member having the necessary strength to pass all of thetests set up by the building codes. It has been proposed to provideacomposite joist containing wooden nailing strips or some nail clinchingfiller material's, or'to pro-- vide a tortuous slot in the top chord forthe revery obviously increase the cost of the joist enormously, andpreclude the use of these joists in the construction of low costhousing.

Another apparent obstacle in the way of using nailable sheet steel inmaking up a joist chord, has been the presumed difiiculty orimpossibility of effecting a satisfactory weld between the Webbing andchord structures of the joist.

The present invention, therefore, in its preferred embodiment,contemplates the provision of an all-steel joist comprising a bottomchord and. web of any suitable or appropriate construction orconfiguration, but embodying a top-chord member of novel and improvedconstruction and properties. The novel top chord is of hollowconstruction requiring no internal filling or reinforcing provisionswhatsoever, the walls of the chord being of sheet steel of a gaugeadapted to be penetrated by a nail or drive screw with no moreexpenditure of energy than that required in driving an eight-pennycommon nail into a wooden joist.

Although formed of nailable sheet stock, the configuration of the novelchord is such that it answers to all of the requirements relating tostructural strength, and it is also adapted to receive the edge of theweb of the joists and to be firmly and permanently resistance-weldedthereto.

Further objects of the invention include the provision of improvedarrangements of bridging, hangers, short span headers, furring supports,end blocking, and other accessories, all made possible by the novelhollow sheet metal topchord member of the joist. v

Other objects and features of novelty will be apparent from thefollowing specification when read in connection with the accompanyingdrawings in which certain embodiments of the invention are illustratedby way of example.

In the drawings,

Figure 1 is a view in side elevation of an end portion of a joistembodying the principles of the invention, some of the sub-flooringapplied thereonbeing shown in section;

Figure 2 is an enlarged view in transverse vertical section taken online 2-2 of Figure 1, and showing to better advantage the noveltop-chord member of the joist;

Figure 3 is a similar view taken on line 3-3 of Figure 1;

Figure 4 is a further enlarged fragmentary sectional view showing themeans for welding the flanges of the upper chord member to the webbingof the joist;

Figure is an enlarged fragmentary view in side elevation of the weldedjoist effected by the means shown in Figure 4;

Figure 6 is a view in side elevation of a joist representing anotherembodiment of the invention;

Figure 7 is an enlarged view in side elevation of an end portion of thejoist shown in Figure 6;

Figure 8 is an enlarged end view of the end bearing portion of the samejoist;

Figure 9 is an end view of a modified form of top-chord member affordingadded structural strength for a given amount of material;

Figure 10 is a similar view of another modification of the top chord;

Figures 11 and 12 are vertical sectional and top plan viewsrespectively, showing theapplication of blocking at the ends of thejoists, particularly in the case of diagonal sub-flooring.

Figure 13 is a fragmentary perspective view of two contiguous joists,illustrating the application of a header member and the supporttherefrom of ceiling furring;

Figure 14 is a view in transverse vertical section through the header ofFigure 13, and taken on the plane I4--I 4 of that figure;

Figures 15, 16, and 17 are top plan, front elevation, and side elevationviews respectively of one of the head-er hangers used in the structureshown in Figure 13;

Figure 18 is a view in vertical section of several adjacent joists suchas occur at a stair well or the like, and showing the novel tensionbridging employed in the preferred form of the invention;

Figure 19 is a fragmentary view in side elevation of a bearing for ajoist at a point remote from the end thereof, a supporting beam beingshown in section; and

Figure 20 is a fragmentary sectional view taken on line 202EI of Figure10.

In Figures 1 to 5 of the drawings there is illustrated one embodiment ofthe invention in which a hollow top-chord member is employed which is ofsuch configuration as to furnish the necessary structural strength eventhough the sheet metal of which the chord is formed, is only of a gaugeequivalent to 18 gauge sheet steel. This type of joist meets allrequirements for relatively short spans, for example joists of saytwelve feet by eight inche and fourteen feet by ten inches, disposed ontwo-foot centers.

The novel joist is indicated in its entirety by the reference numeral l8and comprises the upper chord member II, the lower chord member I2, andthe webbing I3 which supports and connects the two chord members insubstantially parallel spaced relationship. The upper chord member I Isupports a load carrying portion of the building structure exemplifiedby the wooden sub-flooring 2B.

In this embodiment of the invention, the upper chord member is rolled toform an elongated strip of imperforate sheet material having a thicknesswhich when the joist is formed permits the penetration of the upperchord by nails or drive screws such as those indicated at ii].

As most clearly shown in Figures 2 and 3 of the drawings, the upperchord member i formed with an intermediate fiat top wall 2i havingintegrally formed side walls 22 and 23 extending downwardly from theedges thereof and converging toward the center line of the joist, theside walls 22 and 23 preferably being disposed at an acute angle to thetop wall 2|. The lower transversely spaced longitudinal edges of theconverging walls 22 and 23 are extended downwardly to form parallelflanges 24 and 25.

These bottom flanges of the hollow top chord are vertically disposed andlie in spaced parallel vertical longitudinal planes positioned at rightangles to the top wall 2!. Each of the flanges 24 and 25 are of doublethickness, this feature being attained by turning up or lapping thesheet material as clearly shown in Figures 2, 3, and l. Each of theflanges thus comprises the downwardly extending inner walls 26 andupwardly extending outer walls 2?. The lower edges of the flanges 24 and25 thus comprise the rounded return bent portion 28.

The flanges 24 and 25 of the top chord I provide slots for the receptionof the upper edges of the web portions I3 of the joist, these upperedges consisting of the curved portions 29 of the sinusoidally formedwebbing rods 36, these rods extending substantially continuously betweenpoints adjacent the ends of the joist and are preferably of circularcross-section.

In Figures 4 and 5 there is illustrated the means for rigidly connectingthe flanges of the top chord with the webbing rods, this junction beingefifected by pressure or projection welding effected by electricresistance processes. Apair of welding electrodes are indicated at E inFigure 4 of the drawings and it will be readily understood how anapplication of electric current to the welding machine will produce afirm and secure weld between the rods 30 at their upper bends 2t and theinner walls 26 of the flanges 2G and 25. These welds are indicated at 3iin the drawingsr and are preferably of some longitudinal extent beingsubstantially oval or reniform in area. At the same time similar welds32 are formed between the respective Walls 26 and 2i of the flanges 24and 25.

The lower chord member I2 consists of two spaced parallel rods 33 and34, which may be of circular cross-section. These rods rec'e'ive be-'tween them the lower nodes 35 of the webbin rods 30 and are rigidlyfixed to the webbing rods at these points by pressure welds 36. Thelower chord rods 33 and 34 are inclined upwardly at the ends of thejoist as indicated at 35a and the extreme ends of the extensions 35' areagain bent to horizontal position as indicated at 35b. These endportions 351) are welded to an end base plate 31, said end plate beingheld in rigid spaced relation with respect to the end of the upper chordmember I I by a relatively short sinusoidal rod 33 having its lowernodes or curved portions welded to the top surface of the plate 31 asindicated at 38a in Figure 3. The upper nodes of the sinusoidal rod 38are in abutment with the inner side of the upper wall 2| of the topchord member and the intermediate portions of the convolutions of therod 38 are welded to the inner walls of the flanges 24 and 25 asindicated at 3Ia in a similar fashion to the formation of the welds SIwhich unite the webbing I3 with the top chord. If desired, welds mayalso be provided between the end portions 35b of the bottom chord and.the bend in the rod 38 which they embrace. This. arrangement provides asturdy bearing portion. whereby the joist is supported from a wall or:column of a building structure.

The sub-flooring 20 is secured to the upper 4d are driven through thesub-flooring 20. preferably diagonally, so as to pass through each sideportion of the topchord I I, both the top wall 2| and the side walls 22and 23 of the chord being imperforate prior to the afiixing of theflooring, the nails or drive screws thus penetrating the top and sidewalls by their own force and locking in the top chord by means of thefriction aiforded by the inherent slight springiness of the hollow sheetmetal top chord. In this way, no further clinching of the nails orscrews is necessary and the frequently used embedded wooden nailingstrips are also dispensed with.

However, the choice of thickness of the sheet metal of which the topchord is made is rather narrowly limited. If 16 gauge or thicker steelis used the expense naturally rises, and the energy required to drivethe fastening elements through the spaced walls of the top chord wouldbe too great for efficient construction. On the other hand if sheetsteel of a lighter gauge than approximately 18 gauge is employed, whilethe nailing would be accomplished more easily, the top-chord elementwould not have suificient structural strength and rigidity to satisfythe requirements of the building codes. Thus, for practically all sizesof joist coming within the purview of the present invention, thematerial of which the top chords are made is approximately 18 gaugesheet steel, or an equivalent gauge in other suitable metals. Forexample, aluminum alloys and other metals may afford a slightlydifferent gauge of material with the same nailing properties on the onehand and the same self-sustaining structurally rigid properties on theother hand.

The use of sheet metal of the appropriate nailable gauge presents awelding problem in connection with the joining of the web and the topchord. Therefore, the invention provides for thickening the bottomflanges of the top chord and by thus doubling the flanges only of thetop chord member, we have provided a structural element which is shapedto fulfill the requirements of resistance to crushing, twisting, andbending, one which provides for the locking of drive nails for securingthe sub-flooring and other elements to the joist, and an arrangementwhereby a rigid weld may be effected without burning or weakening theconnecting flanges of the top chord.

Although the dimensions of the top chord member may be varied widely inaccordance with the size of the joist, the span to be bridged, and theload to be supported, a joist for the purposes of the one just describedin connection with Figures 1 to 5 of the drawings may have a topchordmember fabricated from a strip of sheet steel about five and one-fourthinches wide. This will provide a top-chord member of a width ofapproximately one and three-fourths inches and will support a load atsay two hundred and forty pounds per lineal foot of the joist, takinginto account live load, dead load, and the required factor of safety.

However, for certain other sizes of joists, for example in the case of ajoist of about twelve inches in depth, and eighteen feet long, the upperchord member may be fashioned from a strip of 18 gauge steel about seveninches wide. larger joists may be made with top sections formed of eightinch strip steel, but in these larger sizes, we have discovered thatcertain further provisions should be made in the construction of thechords and these will be described in Still connection with theembodiments of the inventlon illustrated in Figures 6 to 10 of'thedrawings.

In Figure 6 there is illustrated a joist designated generally by thereference numeral I I0 and which comprises the top-chord member I I I,the bottomchord member U2, and the sinusoidal rod I39 comprising the webportion H3 of the joist. As in the other embodiments the bottom-chordmember IIZ may comprise the two parallel bars I33 and i3 3 and theserods are extended as at I 35 without being brought up to the end bearingportion of the joist. Instead, the end portion of the webbing II3consists of the rod I38 which has a substantially vertical portion I38a,a bend I382, a diagonal part I380, an upper bend I38d and a shortdownwardly inclined end portion I 380. The lower bend I381) is Welded tothe lower chord bars I33 and I34 in the manner previously described andthe welds I3I may be efiected between the flanges of the top chord Hiand the portions of the end rod I38 upon either side of the upper bendI38d. The actual bearing element or shoe for the joist is composed ofthe two angle pieces I31 which embrace the downwardly disposed end I 38aand an intermediate portion of the part title of the rod I38 and weldingis efiected at these points as indicated at I3Ia. It will be readilyseen that by the provision of this novel end bearing structure the samemethod of lateral pressure resistance welding may be employed in unitingthe web rod I35 with the top chord III and the bearing shoes IN, andthis arrangement lends itself to mass production methods.

In order to provide an opening to receive certain tying or anchoringdevices required under some codes, the vertical flanges of the anglepieces it?" may be notched as at I3'Ia.

As mentioned heretofore, additional strengthening provisions are made inthe top-chord memhers which are used in the larger and heavier joists,and which have widths approximating two nches, two and three-eighthsinches, orv greater. Tests have shown that fiat unsupported sections oflight gauge steel structural members should not exhibit a ratio of widthto thickness which exceeds 25 to 1. Therefore, in providing a top chordmember of say seven inch or eight inch blank strip width, and an actualwidth of approximately two inches, a construction such as is shown inFigure 9 of the drawings is provided. Here the top wall I2I of the chordwhich is designated generally by the numeral IIIa is provided with alongitudinally extending bend or depression IEIa which forms an internalbead I2 I b. The

walls I22 and I23 are similar to those described in the case of thefirst embodiment and the depth of the bottom fianges IM and I25 ismaintained at a relatively low dimension in order to conserve materialand also to prevent too great an unsupported straight Width of materialat this point.

As indicated in Figure 8 of the drawings the upwardly extending portionsof certain parts of the webbing structure may abut the inner bead IZIbwhich has the eifect of increasing the innal bracing oi" the joist tosome extent.

In certain cases where wide strips are used in forming the top chordsthe configuration adopted is that shown in Figure 10 of the drawingswhere the cord member I I II) has an internal bead IZic formed in theupper wall I2I thereof and the rather elongated bottom flanges IMa and I25a are doubled in the usual way but then flanged or flared outwardlypreferably at a substantially angle as indicated at I240 and I24d. Thisprovision has the effect of further strengthening the base flanges ofthe chord, andsuflicient length of vertical extent of the flanges [24aand [25b is preserved to effect the welding operation.

Since the I8 gauge dimensions (sheet steel basis) of the box chords ofFigures 8, 9, and 10, is maintained, the same nailing feature isprovided as in the case of the previously described embodiments, and itwill be understood that in all of the illustrations and descriptionswhich follow, in connection with the attachment of various accessoriesto the joists, any of the top chord arrangements illustrated anddescribed herein may be employed, even though the simplest form may bethe one selected for illustration.

In Figures 11 and 12 there is shown an arrangement which is particularlyvaluable in connection with the securing of diagonally arrangedsubflooring. These figures are rather diagrammatic and the end structureof joists fabricated in accordance with the present invention areindicated at I536. The top-chord arrangement HI and the bearing shoeelements l3! will be recognized. The sub-flooring is indicated at I20and it is nailed to the top-chord members III in the usual way. However,in order to provide adequate end support for some of the diagonal piecesof sub-flooring, blocking members 50 are employed, these members 59being lengths of wood spanning the space between the joist ends I60 andhaving edges 51 conforming roughly to the configuration of the sides ofthe joist ends. Fastening elements ifia are driven through the spacedwalls of the chord member HI and thence into the upper corner portionsof the blocking pieces 50. The lower edges of the ends of the blocks areadapted to rest upon the horizontal flanges of the shoes i3? and thevertical dimension of the blocks is approximately the same as the heightof the end bearing portions of the joists, which in most standardizedconstructions is about two and onehalf inches.

In Figure 13 of the drawings there is shown a novel arrangement forsuspending a header member which takes the place of a joist or otherbeam structures for short spans. These headers are adapted to supportthe necessary loads of the structure up to a span of approximately fourfeet. In the illustrated example, the header viii is slung or suspendedbetween two joists H6 and by means of the header hangers 6|.

In order to equip the header so as to facilitate the attachment ofaccessories thereto, the head section or upper chord element of theheader is of exactly the same construction as the top chord members ofthe joists. An inspection of Figure 14 of the drawings will reveal thatthe head section or top chord of the header 60, which is designated bythe reference numeral 2! I, comprises the top wall Hi the downwardlyconverging side walls 222 and 223 terminating in the parallel verticalflanges 224 and 225.

These flanges provide a slot within which is received the upper edge ofthe web MB of the T-member 62. This member is provided with a baseflange 2 l2 and constitutes the lower portion of the header 60.

The header hangers 6| are especially constructed to support a header orother similar element from the top-chord portions of the novel joists,and to do this effectively without subjecting the top chords todistortion or twisting. The hanger 6! is illustrated in detail inFigures 15, 16, and 17. These elements are made of strip steel and areprovided with the outwardly flaring securing wing portions 63 which areprovided with end tabs or flaps 64 adapted to be bent or hooked aroundthe tar edge of the top chord III of one of the joists III], while theangular parts 63 overlie the top wall IZI of the chord. The straps arecontinued down in a vertical plane in front of the top chord as at 65,these portions being of a triangular shape. The downwardly extendingparts of the straps are creased or bent at right angles on the line 61and another triangular portion 58 is disposed in a vertical plane whichis perpendicular to the central plane of the adjacent joists andparallel to the axis of the header 6B which is to be supported. Theremaining tab portions of the straps comprising each half portion of ahanger are bent inwardly into a horizontal position from the areas 68 toform the triangular portions 69 which are disposed beneath the end ofthe header. A rectangular plate 10 is laid upon the tabs or extensions69 and securely welded thereto as suggested at the points H in Figure15. There is thus formed a supporting stirrup or sling which snuglyreceives the header member 50 and is disposed closely to the planes ofboth the header and the joists, allowing plenty of room in the cornersbetween these elements for any other structural elements which it may benecessary to install.

The header hangers 61 are preferably of a slightly heavier gauge sheetmaterial than the material used in making the top chords of the joists.Therefore, the openings 83 in the diverging webs 63 of the hangers mustbe preformed in order to receive the securing elements 75 which take theform of nails or drive screws which are driven through the spacedclinching wall portions of the top chords of the joists.

Another important feature of the hanger involves the wide divergence ofthe wing portions 63 whereby they may be secured around the portions ofthe top chord III of the joists directly above one of the upper bends ornodes of the sinusoidal webbing rod I30 and thus apply the torque to thetop section at these points where it is most rigid.

In Figures 13 and 14 there is shown a very efiective ceiling suspensionmeans applied to the header 69, the timber representing a furringelement of the ceiling to which metal lathing or other supporting meansmay be applied. This element 80 is suspended from the header by means ofthe hanger member designated generally by the reference numeral 82. Themember 82 is made of nailable sheet metal and it consists of an angleshape having its two flanges 83 and 84 extended in opposite directions.The extension 85 of flange 83 is bent around the upper chord 211 of theheader E0 and nailed thereto by means of the nails or drive screws 8'1,the terminal extension 01" the portion 85 being bent around the far edgeof the top chord 2 as indicated at 88 in Figure 14. The downwardextension 89 of the flange 84 is bent around the furring element 88 andmay be secured thereto by means of the nail or drive screw 90. The upperedge 92 of the flange 84 abuts the lower surface of the base flange 212of the header, and the lower edge 93 of the flange 83 abuts the uppersurface of the furring member 89, thus squaring up the suspensionefiectively.

The novel nailable top-chord section provided by the present inventionmakes possible a very simple and efiective bridging means for thejoists. In Figure 18 of the drawings three adjacent joists are shown,two of them being in close juxtaposition to provide double joists asused for example in framing stair wells and the like. Tension bridgingmembers 94 are provided which may consist of approximately 26 gaugestrip steel. If these elements are approximately three-fourths of aninch wide, they will be equivalent in strength to the three-sixteenthsinch around rod bridging which is required by the Steel Joist InstituteCode. One end of these strips is bent around the far side of one of thebottom-chord rods 3 inserted between the rods 33 and 34 comprising thebottom chord l2, and then bent upwardly from beneath the rod 33. Themain portion of the strap St is then brought beneath the rod 33 and,bearine' upwardly against the end portion of the strap, securely snubsthe strap around the bot tom chord of that joist.

The tension strap 94 then continues diagonally upwardly and its upperend is brought over the top of the top-chord member I! of the adjacentjoist where it is securely nailed in position by means of the fasteningelements 95 which pierce spaced walls of the header and are thussecurely held in position as described in connection with the earlierembodiments. Of course, these tension bridging elements are provided toextend from top to bottom chord members of adjacent joists in theopposite directions also. This type of bridging is very quickly andeasily applied, the workmen having merely to snub one end of the striparound the bottom chord member of a joist as shown and then Quickly nailthe other end to the top chord of the adjacent joist, thus veryeffectively lining up the joists and holding them securely in theirproper positions.

In Figure 18, there are also shown furring elements 85 and 86a forattaching lath and plaster around the stair well and at the ceilingportions of the lower story. The ceiling furring piece 55a is readilysecured to the bottom chord 12 of the joist by wiring it in place in theusual way.

Frequently, it is necessary to span a wide building structure by meansof two or more joists arranged endwise, the adjacent ends of the joistsbeing supported by a beam extending at right angles across thestructure. To position this beam or any added superstructure high enoughto immediately underlie the normal shortened end structures of thejoists would dispose the beam or other supports too close to the ceilingnear a partition in some cases, and would prevent the disposal of airconditioning ducts and the like at these points. Therefore, it isproposed to terminate the joists at their inner adjacent ends insections of full height rather than tapering them oil to provide theshorter end sections which normally rest upon the walls or foundations.The joist ends thus may overlap slightly and both rest upon thesupporting beam side by side. In Figures 19 and of the drawings such asupport is illustrated, the beam be-- ing designated 9t and supportingthe bottom chord 12 of the joists Ill through the interme diary of abearing channel 98. This channel is of a width slightly greater than thewidth, of the bottom chord E2 of the joist and is adapted to snuglyreceive the joist and distribute the supporting forces along the joistfrom one lower node of the sinusoidal web rod 39 to the adjacent one,and thus prevent any possible bending or distortion of the rods 33 and34 It will be understood from the above that there has been provided bythe present invention a novel system of supports and suspensions adaptedfor installation even in low-cost housing projects, and which has forits fundamental basis the provision of the novel hollow naiiable sheetmetal heador top-chord element of the joist, beam, or header, which isalso so constructed and arranged as to constitute an effective rigidstructural element and to embody means whereby it may be strongly weldedto the other portions of such joist or similar member.

Various changes and modifications may be made in the embodiments of theinvention illustrated and described herein without departing from thescope of the invention as defined in the following claims. Thus aspreviously indicated, the joists may be made of other sheet metals butof a gauge which is the equivalent of the approximately I8 gauge steelused as a basis of comparison. Also, when drive screws are mentioned inthe application, it is intended to include all equivalent drivenfastening elements having the same frictional holding characteristics.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. In combination, a metal structural element including a web and achord extending along one edge thereof, said chord comprising anelongated, hollow, unfilled, box-like, supporting element havingopposite, spaced apart, angularly related, boundary Walls ofnail-penetrable sheet metal, the cross-sectional configuration of saidhollow chord being substantially triangular, whereby although being ofnail-penetrable metal it is structurally rigid and self-sustaining; acollateral structural member disposed adjacent to and supported by saidchord; driven frictional fastening elements passing through saidcollateral member and also successively through said spaced apartboundary walls, thus passing entirely through said hollow chord; saiddriven fastening elements being retained securely in place by theirfrictional contact with the distorted margins of the openings formed inthe spaced apart boundary walls by the driving of said fasteningelements, combined with the locking effect of the slight deflection ofat least one of said angularly related walls due to the inherent slightunhindered resilience thereof under the driving force of the fasteningelement.

2. The building construction combination as set forth in claim 1 inwhich the structural element is a joist and the hollow chord is the topchord thereof, and in which the collateral structural member is astrap-metal joist bridging member which is of no thicker gauge than thatof the joist chord and is therefore readily nailable to the chord, oneend of said bridging member adapted to be secured to the diagonallyopposite chord of an adjacent joist.

3. The building construction combination set forth in claim 1 in whichthe structural element is a joist and the hollow chord is the top chordthereof, and in which the collateral structural member is a woodenblocking element having a portion disposed beneath one of the lateralportions of the top chord of the joist and in close juxtaposition to theboundary wall of the chord through which one of the driven fasteningele- 11 ments protrudes, so as to be pierced by the end of saidfastening element.

4. The building construction combination set forth in claim 1 in whichthe structural element is a joist and the hollow chord is the top chordthereof.

5. The building construction combination set forth in claim 4 in whichthe collateral structural member comprises a part of the flooringsupported by the joist.

6. In combination, a metal structural element including a web and achord extending along one edge thereof, said chord comprising anelongated, hollow, unfilled, box-like, supporting element havingopposite, spaced apart, angularly related, boundary walls of sheet metalof equivalent strength and penetrability to sheet steel of lessthickness than 16 gauge, the crosssectional configuration of said hollowchord being substantially triangular, whereby although being of suchreadily nail-penetrable gauge it is structurally rigid andself-sustaining; a collateral structural member disposed adjacent to andsupported by said chord; driven frictional fastening elements passingthrough said collateral member and also successively through said spacedapart boundary walls, thus passing entirely through said hollow chord;said driven fastening elements being retained securely in place by theirfrictional contact with the distorted margins of the openings formed inthe spaced apart boundary walls by the driving of said fasteningelements, combined with the looking eifect of the slight deflection ofat least one of said angularly related walls due to the inherent slightunhindered resilience thereof under the driving force of the fasteningelement; said chord having an outer wall and two side walls convergingfrom the edges of said outer wall and having their adjacent edgeslocated at one angle of the substantially triangular crosssection of thechord and spaced slightly apart, a pair of parallel flanges, oneextending from each of the edges of said side walls, said flangesreceiving between them and welded to the edge of said web, said flangesbeing doubled upon themselves'to form a double-ply reinforcing andreadily weldable thickness, and said side walls and outer wall beingsingle-ply.

7. The building construction combination as 12 set forth in claim 6 inwhich said double-ply parallel flanges are bent outwardly intermediatetheir width in opposite directions from the axis of the chord to providedouble-ply winglike strengthening flanges.

AUGUSTINE DAVIS, JR. JAMES A. NICHOLS.

10 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 279,249 Jackson June 12, 1883508,280 Cavallaro Nov. 7, 1893 717,923 Rapp Jan. 6, 1903 813,175 Schaafet a1 Feb. 20, 1906 854,391 Voshardt May 21, 1907 972,525 Francisco Oct.11, 1910 1,046,903 Travalled Dec. 10, 1912 1,253,216 Day Jan. 15, 19181,523,106 Dornier Jan. 13, 1925 1,523,711 Powell Jan. 20, 1925 1,651,032Macomber Nov. 29, 1927 1,729,741 Heltzel Oct. 1, 1929 1,847,891 OttoMar. 1, 1932 1,918,345 McHose July 18, 1933 2,029,645 Waugh Feb. 4, 19362,062,399 Coddington Dec. 1, 1936 2,068,052 Coddington "Jan. 19, 19372,098,676 Rafter -s Nov, 9, 1937 2,099,470 Coddington Nov. 16, 19372,112,480 Coddington Mar. 29, 1938 2,154,520 Mackin Apr. 18, 19392,167,835 Greulich Aug. 1, 1939 2,202,096 Dell et al. May 28, 19402,345,221 Swenson Mar. 28, 1944 2,391,250 Legowik Dec. 18, 1945 FOREIGNPATENTS Number Country Date 164,286 Switzerland 1933 OTHER REFERENCESLight-Gage Flat Rolled Steel in Housing, published by American Instituteof Steel Construction, Inc, received in Patent Ofiice October 26, 1937,pp. 14, 18 and 22. Copy in Div. 33.

